Patent GB-224308-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1923-08-14
Abstract: 224,308. Coventry Automatic Telephones, Ltd., and Collyer, J. E. Aug. 14, 1923. Automatic exchange systems; metering.-A calling subscriber's meter is operated on the reply of the called subscriber by an impulse transmitted over a fourth conductor and measured by the release time of a slow-release relay situated at a connection switch where the transmission bridge is located. During the operation of the connector this relay is utilized as a change-over relay. It also completes the ringing circuit on the energization of the switching relay. When a calling subscriber removes his receiver, his line is extended to an idle connector by a rotary line switch 11, 12, 10, 16, Fig. 1, which operates in the manner described in Specification 208,075. The switching relay 7 at armature 14 prepares a circuit over the fourth wiper 16 for the meter magnet 15. The connector line relay 105, Fig. 2, energizes a slow release relay 107, which grounds the private wire 103 and closes a circuit for the slow release change-over relay 110, over an armature of which dialling tone may be sent. The first impulse series energizes the rotary magnet 113. At the first rotary step the rotary off-normal springs 111 are operated, the relay 120 is energized, and the circuit of the relay 110 is transferred over the vertical off-normal springs 117 and a back contact and armature 115 of the line relay 105, in order that on the cessation of the first impulse series, the relay 110 will relapse and transfer the impulse circuit to the vertical magnet 121. The relay 120 connects the test wiper 123 to the busy relay 124, and on the first vertical step its circuit is transferred to the back contact and armature 115 of the line relay 105. If the wanted line is busy, the relay 124 energizes and locks up, and on the relapse of the relay 120 at the end of the second impulse series, busy tone is transmitted over the armatures 128, 129. If, however, the wanted line is free, on the relapse of the relay 120, a circuit 111, 117, 126, 127 is completed for the switching relay 130, and the called subscriber's cut-off relay is energized over the test wiper 123. A circuit 111, 116, 135, 136, 109 is then completed for the relay 110, which at this time closes a ringing circuit from the generator 138, and at armature 147 closes a further point in the metering circuit. Some ringing current leaks back over the condenser 144 to the calling party. When the called party answers, the ringing cut-off relay 132 energizes, locks up over its lower winding, and extends the called line to the back-bridge relay 145, which at armature 146 completes the metering circuit and at armature 137 breaks the circuit of relay 110, which after an interval falls back and opens the metering circuit. The duration of the metering current is thus equal to the release time of the relay 110. The above meter. ing arrangements may be used in systems employing any number of switching stages, the metering current being sent back from the switch at which the transmission bridge is located. Where the connection is extended over a repeater to a twowire trunk the metering current is transmitted over a fourth wire from the repeater.